Many older adults have difficulty understanding speech in complex and demanding environments of everyday listening. Using laboratory outcome measures, speech-understanding difficulties of older hearing- impaired subjects are accounted for primarily by reductions in speech audibility due to elevated thresholds. Given the importance of speech audibility, amplification provided by a hearing aid should restore important speech information and provide significant benefit to communication. Nevertheless, only a small fraction of older adults who could benefit from amplification own hearing aids and use them regularly. The lack of success and satisfaction with hearing aids suggest that a fundamental change in direction is needed. The design and fitting of communication aids for older adults should be guided by their listening performance in complex and demanding environments that contain the acoustic and perceptual variability inherent in everyday situations. Thus, in this project, a series of experiments is planned to address key questions concerning the perception of speech information by older adults as developed in realistic environments. Aim 2.1 tests the hypothesis that audibility of high frequency interaural level differences and the use of interaural level and timing cues underlie the binaural advantage for speech for older subjects with hearing loss and younger and older subjects with normal hearing. Aim 2.2 using laboratory-based measures and a small hearing aid trial, tests the hypothesis that specific changes in auditory function contribute to reduced benefit from lower and higher frequency amplification for older subjects and may related to their hearing aid use and success. Aim 2.3, using psychophysical measures and a functional brain imaging paradigm, tests the hypothesis that age-related changes in auditory selective attention increase the effects of stimulus uncertainty, especially in adverse listening conditions. A long-term goal is to extend our general understanding of mechanisms that account for reduced speech understanding in noise by older adults and thus enhance benefit derived from amplification.